> Twitter does set a title tag and thus that tag should be within a head block.
It is in a <head> element. You don’t understand how HTML is parsed. The opening and closing tags for the <head> element are optional. That doesn’t mean the element isn’t there, it means that the element is always there.
> They are leaning on browser compatibility mode to cover the fact that they aren't adhering to standards.
They aren’t. See this comment I made and go ahead and paste that HTML into a validator:
https://news.ycombinator.com/item?id=30475015
There is no error handling taking place, there is no browser compatibility mode involved. This is correct HTML that adheres to the standard being parsed normally.
> [1], [2], [3]
Why are you quoting a style guide written in 1992 and two unofficial sources when you could just as easily have referred to the actual HTML specification?
> § 13.1.2.4 Optional tags
> Certain tags can be omitted.
> Note: Omitting an element's start tag in the situations described below does not mean the element is not present; it is implied, but it is still there. For example, an HTML document always has a root html element, even if the string <html> doesn't appear anywhere in the markup.
— https://html.spec.whatwg.org/multipage/syntax.html#syntax-ta...
The HTML specification literally gives this as an example of a valid document:
<!DOCTYPE HTML>
<title>Hello</title>
<p>Welcome to this example.</p>
There are a great many ways in which people write broken HTML and the browser repairs things. This is not one of them. Omitting the opening and closing tags for the <head> element is perfectly correct HTML that adheres to the standard.